妊娠－泌乳母猪钙代谢及调控机理研究进展

母猪的生产性能受很多因素的影响，其中日粮矿物质水平是其主要影响因素之一。钙在调控母猪的生产性能方面发挥着重要的作用。机体钙吸收的方式有3种，即主动转运、被动转运和囊泡运输，激素或者其他影响钙吸收的因素大多是通过调控钙吸收方式进而影响日粮钙的利用率。母猪对日粮钙的利用率直接影响其生产性能的发挥，一方面，适当的日粮钙水平可以促进母猪发挥最大的生产潜能，提高养殖效益；另一方面，当日粮钙水平不足或者钙利用率低时，首先，母猪的生产性能潜力不能充分发挥，如产仔数或活仔数低，仔猪的生长速度慢。其次，母猪由于钙利用不足而导致骨骼疾病的发生，尤其是妊娠后期和哺乳期的母猪，最终使其淘汰率居高不下，这一系列的因素最终导致养殖业的生产效益大幅度降低。近年来，国内外学者针对影响母猪对日粮钙利用率的因素进行了大量的研究，并取得了很大的进展，例如，钙的饲喂时间、日粮钙磷比、维生素、激素和消化道pH均影响母猪对日粮钙的吸收利用。因此，研究母猪钙吸收特征及其影响因素对提高母猪生产性能具有重要的实践意义。作者简述了机体钙吸收的作用机制，同时介绍了影响母猪钙吸收的主要因素，旨在为母猪日粮钙的饲喂提供理论依据。     

葡萄糖转运蛋白的研究进展

存在于肠道、肾近端小管的葡萄糖转运载体对葡萄糖的吸收和重吸收具有很重要的作用。其中肠道葡萄糖主要是通过位于肠细胞膜上Na —依赖性葡萄糖转运载体(SGLT1)进行主动转运的。从十二指肠到回肠的肠轴上分布有不同的SGLT亚型,这些转运载体对葡萄糖和半乳糖的转运能力与它们的     

妊娠-泌乳母猪钙代谢及调控机理研究进展

母猪的生产性能受很多因素的影响,其中日粮矿物质水平是其主要影响因素之一。钙在调控母猪的生产性能方面发挥着重要的作用。机体钙吸收的方式有3种,即主动转运、被动转运和囊泡运输,激素或者其他影响钙吸收的因素大多是通过调控钙吸收方式进而影响日粮钙的利用率。母猪对日粮钙的利用率直接影响其生产性能的发挥,一方面,适当的日粮钙水平可以促进母猪发挥最大的生产潜能,提高养殖效益;另一方面,当日粮钙水平不足或者钙利用率低时,首先,母猪的生产性能潜力不能充分发挥,如产仔数或活仔数低,仔猪的生长速度慢。其次,母猪由于钙利用不足而导致骨骼疾病的发生,尤其是妊娠后期和哺乳期的母猪,最终使其淘汰率居高不下,这一系列的因素最终导致养殖业的生产效益大幅度降低。近年来,国内外学者针对影响母猪对日粮钙利用率的因素进行了大量的研究,并取得了很大的进展,例如,钙的饲喂时间、日粮钙磷比、维生素、激素和消化道pH均影响母猪对日粮钙的吸收利用。因此,研究母猪钙吸收特征及其影响因素对提高母猪生产性能具有重要的实践意义。作者简述了机体钙吸收的作用机制,同时介绍了影响母猪钙吸收的主要因素,旨在为母猪日粮钙的饲喂提供理论依据。     

单胃动物小肠内可消化性碳水化合物的吸收及其调控

本文阐述单胃动物小肠内可消化性碳水化合物的吸收及其调控机制。可消化性碳水化合物在单胃动物体内的降解产物主要为葡萄糖、果糖、半乳糖和双糖。葡萄糖、果糖和半乳糖在小肠内,由小肠内绒毛上皮细胞或细胞间隙直接吸收;双糖在双糖酶的作用下水解成单糖形式,为小肠绒毛上皮细胞吸收。其吸收机制可分为3个途径:主动吸收、被动吸收以及通过细胞间隙直接吸收。其中主动吸收是主要的吸收途径。调控小肠可消化性碳水化合物吸收的因素较多,包括吸收面积、Na 电化学梯度、细胞膜脂质成分、转运细胞与非转运细胞比例、转运子周转速率、亲和系数等因素。通过多种因子的调控作用,能有效地促进碳水化合物的吸收,以满足动物体的生长和发育的需要。     

矿物质营养素在动物养殖中的作用

正1吸收和代谢饲粮矿物元素转变为离子,并且通过主动或被动方式从动物胃肠道吸收。主动吸收是指矿物元素通过肠壁由肠腔泵入肠细胞的吸收过程。主动吸收的矿物质元素包括Ca、P和Na。通常主动吸收是逆浓度梯度进行的,即矿物质由低浓度被泵到高浓度,在这一过程中要消耗能量。然而,大部分矿物质的吸收是以被动吸收方式进行的,即元素通过胃肠道表层从高浓度流向低浓度。因此被动吸收的数量受到饲料中和体内元素浓度的影响很大。矿物元素主要以离子形式     

寡肽的营养研究新进展

过去一直认为蛋白质必须水解为游离氨基酸才能被吸收。其实，大量寡肽可 逃脱被消化成游离氨基酸的命运，而直接以肽的形式吸收进入体循环。 最近一二十年来，对肽的营养研究主要集中在寡肽的吸收机制，寡肽与游离氨基酸 吸收的关系，蛋白质在消化过程中寡肽的释放规律，寡肽的转运和代谢规律，寡肽对内分泌 、氮沉积、组织蛋白质周转代谢的作用和影响，肽的生理活性作用。通过研究，对肽的代谢 特点和营养作用已有了许多新的认识。 1 寡肽的吸收机制及其特点 血液循环中肽类的来源主要有以下几种方式：①消化道吸收；②机体合成；③体蛋 白分解；④肠外营养方式，如皮下、肌肉、静脉注射含二肽的氨基酸溶液；⑤服用具有肽类 结构的药物。其中第一种是血液循环获得肽类最主要的方式（Adibi,1997）。 寡肽的吸收机制与游离氨基酸完全不同。游离氨基酸的吸收是一个主要依靠Na ＋ 泵的主动转运过程，而寡肽的吸收是一个主要依赖H＋或Ca2＋离子浓度电导而进 行的消 耗能量的转运过程。大多数寡肽的吸收和转运需要一个酸性环境，1分子肽需2个H＋ 。肠粘膜上存在肽的转运载体。 Daniel(1994)认为，肽载体转运能力可能高于各种 氨基酸载体转运能力的总和。     

饲用小肽产品的生产工艺

小肽吸收机制与氨基酸不同，小肽的吸收主要依赖H^＋浓度或Ca^2＋离子浓度电导．是低能量消耗，逆浓度梯度转运过程，它不同于肠细胞游离氨基酸的主动运转过程，后者耗能高，易饱和，吸收速度慢。动物吸收蛋白质主要以小肽形式吸收，小分子活性多肽转运系统具有耗能低而不易饱和的特点，其吸收速度较快。     

无机盐和水吸收的生理机制

1钠离子的吸收 钠占体液阳离子总量的90%以上，肠内容物中95%-99%的钠均可被吸收。小肠各段都能吸收钠，但空肠对钠离子的吸收最快，回肠较慢，结肠更慢。钠协同转运系统，即与葡萄糖、氨基酸等相协同的主动转运系统。钠、氯同时吸收，此机制可能是由于在肠黏膜上皮细胞存在着与钠、氯转运有关的两个独立的离子转运系统。为发动此过程，肠上皮细胞内的水和二氧化碳在碳酸酐酶的作用下生成碳酸，后者很快分解成氢离子和碳酸氢根离子，细胞膜上的一个离子通道进行氢离子和钠离子交换，同时，另一个通道进行碳酸氢极离子和氯离子的交换。因为氢离子和碳酸氢根离子以相同的速度透出细胞，所以肠上皮细胞内的pH值保持不变，进入肠腔中氢离子和碳酸氢根离子又重新合成碳酸。进入细胞内的钠离子被钠泵酶主动转运至细胞间隙，氯离子则在细胞内蓄积并通过上皮细胞基底膜上的特殊通道排入细胞间隙。钠和氯的吸收速度取决于氯通道的通透性，通透性大，氯能很快离开上皮细胞，允许氯的继续吸收。此机制在回肠和结肠较为活跃。钠离子的单纯扩散，正常情况下肠腔内和血液内钠离子的浓度都是150毫摩尔/升，而肠上皮细胞内钠离子的浓度是15毫摩尔/升，钠离子可以顺电化学梯度通过扩散作用进入细胞内。而细胞内的钠离子通过基底膜进入血液则是逆电化学梯度进行的主动转运过程，此过程由钠泵钠泵协助进行，并由三磷酸腺苷分解供能。     

生长猪小肠钠依赖型磷摄入特性的研究

选取6头体重接近的3月龄生长期大白猪,屠宰后刮下肠黏膜,提取3段小肠上皮细胞刷状缘膜囊泡(Brush-border membrane vesicles,BBMV)。在室温条件下,研究各段小肠BBMV磷的摄入量,pH和钠离子依赖性,并测定BBMV磷吸收动力学参数。结果表明,生长猪BBMV对磷的主动吸收和被动扩散在酸性pH下均受到抑制。钠离子水平影响BBMV磷的主动吸收。pH7.4条件下,测得钠依赖型磷转运系统Hill系数(napp)为2.07,即转运1个磷酸根,至少有2个钠离子与其协同转运。不同肠段BBMV磷的主动吸收并没有显著差异。pH7.4条件下,生长猪钠依赖型磷转运系统对磷的亲和力常数(Km)为(0.43±0.09)mmol/L。最大转运速度(Vmax)为(2.25±0.19)nmol/(mg蛋白.15 s)。     

家兔小肠不同区段营养物质转运载体相关基因的分布规律

旨在研究家兔小肠不同区段营养物质转运载体相关基因的分布规律。本研究选取110日龄体重相近的健康白色獭兔10只,屠宰后采集十二指肠、空肠、回肠样品,采用real-time PCR研究家兔不同肠段小肽转运载体Pep T1,氨基酸转运载体CAT1、B~0AT、EAAT3、rBAT,葡萄糖转运载体SGLT1、GLUT2、GLUT5,以及脂肪酸转运载体FATP4的mRNA表达丰度。结果显示,小肽转运载体Pep T1 mRNA在十二指肠表达量最高,空肠略低;碱性氨基酸转运载体CAT1、兼性氨基酸转运载体rBAT和中性氨基酸转运载体B~0AT mRNA的表达量均在回肠最高,空肠次之;酸性氨基酸转运载体EAAT3 mRNA的表达量在空肠和回肠均较高;葡萄糖转运载体SGLT1和GLUT5 mRNA的表达量在十二指肠和空肠均较高;葡萄糖转运载体GLUT2和脂肪酸转运载体FATP4 mRNA的表达量则是空肠最高,十二指肠次之。结果表明,家兔肠道转运吸收小肽、葡萄糖和脂肪酸的主要部位是小肠前半段,转运吸收氨基酸的主要部位是小肠后半段。     

Effects of bisphenol A administration to pregnant mice on serum Ca and intestinal Ca absorption

Bisphenol A (BPA) is a xenoestrogen commonly used in food storage plastics. The present study was conducted to clarify the effects of BPA administration to pregnant mice on serum calcium (Ca) and Ca metabolism of the gut and kidney. From 6.5 to 16.5 days post coitus (dpc), pregnant mice were administered at 2 mg or 20 mg/kg body weight/day of BPA. Serum Ca was decreased in mice treated with 20 mg BPA at 17.5 dpc, but no remarkable differences were detected in the alkaline phosphatase activity and vitamin D receptor protein expression in the duodenum and jejunum. The messenger RNA (mRNA) expressions of calcium binding protein (CaBP‐9k) and active vitamin D synthesis enzyme (CYP27B1) in the kidney were increased in mice treated with 20 mg BPA. The mRNA expressions of occludin and junction adherence molecular A (JAM‐A) in the duodenum and ileum, which regulate paracellular transport, were increased in mice treated with 20 mg BPA. However, the administration of 2 mg BPA had no effect on serum Ca and mRNA expressions of relative genes in Ca metabolism. These results imply that BPA administration at 20 mg/kg body weight/day during pregnancy decreases serum Ca in pre‐delivery mice, which may be partly due to decreased paracellular Ca absorption.     

Electrophysiologic changes in rumen epithelium in their effect on magnesium transport--a review

The forestomach is the main site of Mg2+ absorption in the gastrointestinal tract of ruminants and maintains Mg2+ homeostasis. It has long been known that an increase in K+ intake and, consequently, in ruminal K+ concentration ([K+]) decreases the apparent digestibility of Mg2+, which increases the risk of hypomagnesemia and tetany. The present review summarizes new findings on the mechanisms of Mg2+ absorption across the rumen epithelium. It has been shown that transcellular and active Mg2+ transport is the predominant pathway for Mg2+ transport from lumen to blood. It is well established that the apical uptake of Mg2+ is mediated by a PD-independent of K(+)-insensitive and by a parallel working PD-dependent, K+ sensitive mechanisms. The predominant driving force for the electro-diffusive Mg2+ uptake is PDa, the potential difference across the apical membrane of the rumen epithelium, that amounts to -50 mV under physiological conditions, permitting an effective Mg2+ absorption even at very low luminal Mg2+ concentrations. The antagonism between K+ and Mg2+ absorption can be explained by K+ dependent electrophysiological changes of the rumen epithelium. An elevation of the ruminal [K+] has two different effects that are responsible for the observed reduction of net Mg2+ absorption; (1) It depolarizes PDa and thereby reduces the driving force for the electro-diffusive Mg2+ uptake into the ruminal epithelial cells, hence decreases the cytosolic [Mg2+] and the transcellular component of Mg2+ absorption; (2) It increases the transepithelial potential difference (PDt; blood-side positive) and, hence causes a small, passive backflow of Mg2+ via the paracellular route from the blood side into the lumen. The second, PD-independent uptake mechanism is primarily working at high ruminal [Mg2+]. Therefore the negative effect of K+ can be compensated by this K+ insensitive Mg2+ absorption, if high [Mg2+] are present in the ruminal fluid.     

动物的肽吸收机制及组织利用

已有的研究证实,小肽的消化道吸收机制不同于氨基酸。已发现的吸收机制包括渗透扩散、中间载体转运、通道穿透吸收3种方式。其中,小肽的中间载体转运吸收有2种类型:(1)依赖跨膜的H 浓度梯度,H /肽共转运子在向吸收细胞内转运分子肽的同时伴随着两个H 的吸收,而跨膜的H 浓度梯度则是依靠耗能的Na /H 交换子来维持,H /肽共转运子和Na /H 交换子在功能上是独立的;(2)肽中间载体转运依赖跨膜的阳离子浓度梯度,而二价阳离子的促吸收作用高于一价阳离子。已知谷胱甘肽是通过第二种转运机制转运的。瘤胃和瓣胃具有很强的小肽吸收能力,可能是反刍动物肽吸收的主要部位,但有关研究的结果差异较大,与动静脉差法的测定误差较大有关。对于体组织肽利用的了解不多,已有的研究表明体组织可以利用小肽,其过程是组织吸收的肽在组织细胞内降解为氨基酸,而后用于蛋白质的合成和分解代谢。     

Transport of nutrients and electrolytes across the intestinal wall in pigs

In recent years, intestinal transport processes have been studied in detail regarding both, functional and structural aspects. For monosaccharides different systems have been demonstrated for apical uptake: this includes the high-affinity SGLT1 as a distinct d-glucose system and GLUT5 for fructose. Specifically in pigs a low affinity, high-capacity system for d-glucose and d-mannose with no preference for Na⁺ over K⁺ and a very low affinity system are suggested as further uptake systems. As in other species, basolateral extrusion is mediated by GLUT2. The distributions of monosaccharide transport along the gastrointestinal axis as well as the potential role of paracellular monosaccharide absorption have not yet been clarified.

Amino acids can principally be absorbed by the paracellular and transcellular pathway whereas transcellular transport can either be mediated by facilitated diffusion or secondary active Na⁺-coupled transport. This includes different transport systems for neutral, anionic and cationic acids. In addition, the presence of the di-/tripeptides transport system PEPT1 which depends on an inwardly directed H⁺-gradient has also been confirmed for the pig small intestine, its quantitative proportion is still under debate.

Short chain fatty acids (SCFA) are the major end products of microbial carbohydrate fermentation which occurs along the gastrointestinal tract with the highest production rates in the large intestines. At least two uptake mechanisms have to be assumed, i.e., non-ionic diffusion and anionic exchange via SCFA⁻/HCO₃⁻-exchange. Controversial views still exist to what extent SCFA are metabolized within the epithelial tissue.

Segmental differences between small and large intestines have been demonstrated for Na⁺ absorption. Whereas in the small intestines the major part of Na⁺ absorption is mediated by coupled nutrient transport systems, aldosterone sensitive Na⁺ channels and Na⁺/H⁺-exchange are the dominant mechanisms in the hindgut. For Cl⁻ paracellular transport and anionic Cl⁻/HCO₃⁻-exchange are the major absorptive mechanisms. Cl⁻ secretion is mediated by apical channels which may be activated by toxins of different origin. Different types of Cl⁻ channels have been identified, such as Cystic Fibrosis Transmembrane Regulator (CFTR), Ca-activated Cl⁻ channels (CLCA) and Outwardly Rectifying Cl⁻ Channels (ORCC). Whereas CFTR has clearly been shown for jejunal and colonic epithelial and goblet cells controversy still exists on the relevance of CLCA and ORCC in pigs.

For Ca²⁺ there is evidence that both recently published channels TRPV5 and TRPV6 are also expressed in pig intestinal tissues, however, this has not yet been shown on protein level. From several functional approaches it was demonstrated that phosphate uptake can be mediated by both, a Na⁺-dependent transcellular component and paracellularly. On a molecular basis it is uncertain whether the transport protein of transcellular mechanism belongs to the NaPi-IIb cotransporter family.     

Influence of food deprivation on the transport of 3-O-methyl-alpha-D-glucose across the isolated ruminal epithelium of sheep

Recent studies provided evidence that the ruminal epithelium is able to absorb D-glucose even at physiologically low intraruminal concentrations. To elucidate whether ruminal D-glucose transport shows adaptive responses during food deprivation, transport of 3-0-methyl-alpha-D-glucose (3-OMG), a hardly metabolizable D-glucose analogue, was measured in isolated ruminal epithelia obtained from hay-fed or food-deprived adult sheep. In both groups, a significant net absorption of 3-OMG to the serosal side (in vivo: blood side oriented) could be detected at 3-OMG concentrations between 0.25 mM and 5 mM. Net absorption of 3-OMG was abolished by mucosal (in vivo: lumen side oriented) addition of phlorizin, an inhibitor of the sodium glucose-linked transporter 1 (SGLT-1). Net absorption of 3-OMG followed Michaelis-Menten kinetics, but apparent affinity and maximal transport capacity were lower in epithelia obtained from food-deprived sheep. In contrast to the decrease of the (secondary) active 3-OMG transport, serosal-to-mucosal permeation of 3-OMG increased after food deprivation, suggesting an elevated passive 3-OMG transfer. It is concluded that the altered transport characteristics are either part of a global energy-sparing process during food deprivation (i.e., a lowered activity of the Na+/K+-ATPase) or result from specific down-regulation of SGLT-1.     

Caco-2细胞模型及其在营养素小肠吸收机理研究中的应用

Caco-2细胞源自人结肠癌细胞,体外培养时能自发地进行类似肠道细胞的形态学和生化学上的分化,获得许多小肠吸收细胞的特性,如形成微绒毛结构;在细胞表面形成良好的刷状缘;在细胞间形成紧密连接;分泌水解酶以及合成转运糖、氨基酸和药物等的载体转运系统。由培养在微孔滤膜上的Caco-2细胞构建的模型为研究营养素在小肠的吸收机理提供了一个有效且易于操作的实验手段。本文主要综述了Caco-2细胞模型的建立、特征、检测及其在氨基酸、维生素、核苷和微量元素等营养素小肠吸收机理研究中的应用。